This application claims priority to German Patent Application No. 10 2013 210 168.6 filed on May 31, 2013, the entirety of which is incorporated by reference herein.
This invention relates to a structural assembly for a fluid-flow machine.
The aerodynamic loadability and the efficiency of fluid-flow machines, in particular of fluid-flow machines such as blowers, compressors, pumps and fans, is limited by the growth and the separation of boundary layers in the rotor and stator blade tip area near the casing or the hub wall, respectively. On blade rows with running gap, this leads to high secondary losses and possibly to the occurrence of operational instabilities at higher loads.
A known counter-measure is to use so-called casing treatments. The simplest form of casing treatments are circumferential grooves having rectangular or parallelogram-shaped cross-sections, as disclosed for example in EP 0 754 864 A1. Other solutions provide for rows of slots or openings in the casing, with the individual slots/openings being oriented substantially in the flow direction and having a slender form with a small extent when viewed in the circumferential direction of the machine. Solutions of this kind are disclosed for example in DE 101 35 003 C1.
Further casing treatments include provision of a ring over the entire circumference in the area of a rotor in the casing, with stator vanes often being provided to reduce the flow swirl inside the treated casing, as for example described in the publications EP 0 497 574 A1, US 2005-0226717 A1, U.S. Pat. No. 6,585,479 B2, US 2005-0226717 A1 and DE 103 30 084 A1.
Existing concepts for casing treatments in the form of slots and/or chambers in the annular duct wall offer increased stability of the fluid-flow machine. This is however only achieved with a loss in efficiency due to the unfavourably selected arrangement or shape. Known solutions also take up a large installation space at the periphery of the annular duct of the fluid-flow machine, and due to their shape (e.g. simple parallelogram-shaped circumferential casing grooves) they are only of restricted effectiveness and are always provided in the casing in the area of a rotor blade row. Casing treatments according to the state of the art are intended for easy implementation in the casing from an accessible side with the aid of machining, usually metal-cutting.
The use of injector systems is known as a further counter-measure against secondary losses and the occurrence of operational instabilities. For example, it is known from U.S. Pat. No. 8,152,445 B2, to pass fluid from a fluid supply chamber into the flow duct by means of a nozzle system. FIG. 1 shows the solution described in U.S. Pat. No. 8,152,445 B2. A disadvantage of this solution is that a complex secondary flow duct system for fluid injection in the area of the casing or hub must be provided by specific design and production measures.
A fluid-flow machine is known from DE 10 2008 037 154 A1, which has, in the area of the blade leading edge in a main flow path boundary, at least one secondary flow duct connecting to one another two openings arranged on the main flow path boundary. Each secondary flow duct connects one discharge opening to a supply opening provided further upstream. The provision of secondary flow ducts of this type permits effective influencing of the boundary layer in the blade tip area and hence allows an increase in the stability of a fluid-flow machine, without the need for an expensive casing treatment over the entire casing circumference in the area of a rotor. However, complex secondary flow ducts in the area of the casing or hub can only be achieved by specific design and production measures.